1. Field of the Invention
The present invention relates to a charging device including a cleaning member configured to clean a grid electrode and a shutter configured to cover an opening of a corona charger.
2. Description of the Related Art
Conventionally, there are known image forming apparatuses employing an electrophotographic method and using a corona charger in a charging process. Some corona chargers of such image forming apparatuses are known to have a grid electrode provided at an opening portion of a shield thereof to stabilize electric potential of a photosensitive member.
However, foreign matters, such as airborne toner particles, tend to accumulate on the discharge side of the grid electrode. When such foreign matters locally accumulate on the inner surface of the grid electrode, defective charging tends to occur at the portion corresponding to where the foreign matters have accumulated.
Japanese Patent Application Laid-Open No. 2005-338797 discusses a configuration that prevents foreign matters from accumulating locally on the grid electrode by providing a cleaning unit that cleans the inner surface (discharge wire side) of the grid electrode. To be more precise, while a cleaning brush as a cleaning member is in contact with the inner surface of the grid electrode, the cleaning brush is driven in the longitudinal direction of the grid electrode. In this manner, the inner surface of the grid electrode is cleaned.
The corona charger is known to generate corona products such as ozone (O3) and nitrogen oxide (NOX) when charging the photosensitive member.
When the corona products are attached to the photosensitive member, and the attached corona products absorb moisture, the surface resistance of a portion to which the corona products have attached is reduced. Under the condition where the corona products having absorbed moisture are attached to the photosensitive member, an electrostatic latent image which corresponds to the image information cannot be accurately formed, and a defective image called “image deletion” is generated.
To solve such a problem, Japanese Patent Application Laid-Open No. 2007-072212 discusses a configuration that includes a shutter for covering an opening of a corona charger, so that the occurrence of the image deletion is reduced.
In a state where the image formation is not performed (e.g., at nighttime or when the main body is powered off), the opening of the corona charger is covered. Before the image forming is performed, the closed shutter is opened. The user generally desires quick start-up of the image forming apparatus, thus requiring enhancement of the shutter-opening speed.
In the configuration where both the shutter and a grid cleaning member are driven in the longitudinal direction of the corona charger, it is desirable to use one drive source (motor) for driving both the shutter and the grid cleaning member, from the viewpoint of cost reduction.
However, in the configuration where one drive source is shared, when the shutter is always quickly opened for the purpose of reducing the start-up time, the grid electrode may not be sufficiently cleaned by the cleaning member. More precisely, if the shutter and the cleaning member are always moved quickly for the purpose of reducing the start-up time of the image forming apparatus, the photosensitive member may not be uniformly charged due to insufficient cleaning of the grid electrode, and a defective image may be formed.